1. Field of the Invention
The present invention relates to a fuel cap for a filler opening of a fuel tank mounted on a vehicle, such as automobile.
2. Description of the Related Art
In general, vehicles are equipped with a fuel tank for storing fuel. Fuel caps are known for covering a filler opening of the filler neck of the fuel tank.
FIG. 6A shows a perspective view of a cap member included in a conventional fuel cap, and FIG. 6B shows a front view of the conventional fuel cap. As shown in FIG. 6B, the fuel cap C1 includes the cap member 100 (see FIG. 6A) and a screw member 200, and a thread 200a is provided on the outer periphery of the screw member 200. The thread 200a is capable of engaging with a filler neck thread F2 on an inner wall of a filler opening F1 of a filler neck F connected to a fuel tank (not shown). To the upper portion of the screw member 200, a gasket G for sealing is attached in such manner that it is covered with the cap member 100.
The fuel cap C1 having such a construction can be fitted on the filler opening F1 through the engagement of the thread 200a of the screw member 200 with the filler neck thread F2 on an inner wall of the filler opening F1. When the fuel cap C1 is fitted on the filler opening F1, the gasket G is brought into close contact with a sealing surface F1′ of the filler opening F1, thereby sealing the filler opening F1 (for example, see Japanese patent publication No. 3389850, paragraphs 0011-0012 and FIG. 1). The obtained sealing of the filler opening F1 avoids evaporation of the fuel from the filler opening F1.
In addition, a fuel cap equipped with a device for monitoring the closing position of the cap member has been disclosed for the purpose of securing the closure of the fuel cap (for example, see U.S. Pat. No. 6,206,219B1, column 2, line 46—column 3, line 52 and FIG. 1).
In general, when the above-mentioned conventional fuel cap C1 is fitted on the filler opening F1, the fuel cap C1 is screwed in until the sealing with the gasket G is secured in order to prevent the fuel from evaporating from the filler opening F1.
Except for refueling event or the like, the fuel cap C1 is usually kept fully screwed in the filler opening F1, and thus the gasket G is subjected to vertical compression for a long period of time. This may result in deformative weakening of the gasket G, as shown in FIG. 7, which in turn may cause the loss of sealability at the filler opening F1. To compensate this loss, the fuel cap C1 should be further screwed in.
However in the conventional fuel cap C1, a terminal part 210 of the thread 200a is formed so that it is connected with a rib 220 which prevents the gasket G from being detached. For this reason, when an attempt is made to further screw the fuel cap C1, an end part F2′ (shown with a broken line in FIG. 7) of the filler neck thread F2 hits the connected part, and the fuel cap C1 is hindered from being further screwed, resulting in poor seal-ability.
Therefore, it would be desirable to provide an improved fuel cap that can attain effective sealability regardless of the state of the gasket.